Ultrahigh molecular weight polyethylene (“UHMW PE”) is well-known for, among other properties, its chemical resistance, low friction coefficient, high toughness and in particular its excellent resistance against wear. As a result, it has found numerous applications in environments where abrasion and friction may occur, such as in the chemical industry, mining, mechanical engineering, the field of biomedical implants and the textile industry. Equally well-known, however, is the intractability of this polymer, which is due to the fact that UHMW PE, above its crystalline melting temperature, does not form a fluid phase that is of a viscosity that permits melt-processing techniques used with many thermoplastic polymers. Commonly, the viscosity of UHMW PE is above 106 Pa.s at 180° C. Due to this high viscosity, UHMW PE is processed into shapes and objects with techniques that are dissimilar to melt-processing methods. Rods, sheets, blocks, slabs and profiles of UHMW PE are produced by cumbersome methods such as, for example, ram-extrusion, pre-forming and sintering of compressed powder, optionally followed by machining or skiving, high isostatic pressure processing, and the like. Unfortunately, these methods generally are less economical than common melt-processing, and, in addition, severely limit the types and characteristics of objects and products that can be manufactured with this polymer.
The above drawback of UHMW PE has long been recognized and techniques have been developed to circumvent the intractability of this material by, for example, adding solvents, lubricants, plasticizers, processing aids, as well as certain polyethylenes of lower molecular weight. See, e.g., U.S. Pat. Nos. 5,658,992 and 5,422,061. The aforementioned additions of lubricants, plasticizers, and processing aids or lower molecular weight polyethylenes, however, do not yield melt-processible PE compositions with a desired combination of properties.